Existing gripper type material feeding devices utilize a movable linearly guided gripper mechanism for intermittently feeding a workpiece to a stamping machine. Some such gripper type feeding devices typically utilize a cam for the actuation of the feeding motion. Such devices are exemplified in U.S. Pat. No. 6,283,352 and U.S. Pat. No. 6,213,369. Such devices utilize a rotary oscillating cam mechanism with a fixed rotation angle, a lengthwise adjustable driving member attached to the actuator, and a linkage arrangement or other transmission elements between the actuator and the gripper mechanism. The lengthwise adjustable driving member comprises mechanical adjusting components for changing the index distance of the feed apparatus and the workpiece. The disadvantage of such arrangements is that the mechanical adjustments are complex and inconvenient.
Other existing gripper type material feeding apparatus utilize a pneumatic or a hydraulic cylinder for the actuation of the feeding motion. Typically an adjustable mechanical stop is provided for changing the index distance of the feed apparatus and the workpiece. An example of such device is seen in U.S. Pat. No. 5,505,360. The disadvantage of such devices is that adjustment of the mechanical stop is inconvenient. Furthermore, the pneumatic or hydraulic cylinder used in such devices suffers from a speed limitation due to the slow response of this type of such actuators.
Other existing gripper type material feeding apparatus utilize a pneumatic or a hydraulic cylinder for the actuation of the feeding motion, chain and sprocket transmission elements for converting the linear motion of the cylinder into a rotary motion of a driving member, fixed stops on the rotating driving member, connecting links, and mechanical adjusting components for the lengthwise adjustment of the connection distance of the driving member to the connecting link. An example of such device is seen in U.S. Pat. No. 4,577,791. A disadvantage of such a device is that the device and the mechanical adjusting components are complex, inconvenient and high maintenance. Furthermore, the pneumatic or hydraulic cylinder used in such feeding apparatus suffers from a speed limitation due to the slow response of this type of actuator.
Still other existing gripper type material feeding apparatus utilize a reversible motor, lead screws and threaded bushings for the actuation of the feeding motion. An example of such a device is seen in U.S. Pat. No. 5,909,835. The disadvantage of this device is that a large angle of rotation of the motor is necessary due to the nature of lead screw and threaded bushing transmission elements. The operational speed of such a device is therefore limited. Furthermore, this type of feeding device suffers from high wear characteristics and high maintenance costs.
There exists then the need for a gripper type material feeding apparatus which does not require mechanical adjustments for changing the feeding distance of the feeding device or the workpiece, is suitable for operating at high index cycle rates, and is low maintenance.